Thirteen years ago, Hurricane Katrina hit New Orleans. Floodwaters from the storm breeched the city’s levee system, letting billions of gallons of water into the city and killing over a thousand people. Since then, federal, state and municipal governments have implemented improvements to the city’s drainage and levee systems. There is still a real risk that these water management systems might not be enough for the next big storm. Unfortunately, we won’t know until it happens.
Water, Water Everywhere
Because New Orleans is largely below sea level and has a rainy climate, it relies on two systems to stay above water level: a 192-mile-long flood prevention system of levees and floodwalls, and a complex system of pipes and pumps to get the water out of the city once it’s in there.
The flood barriers are the more well-known part of the city’s defenses, though not always for the right reasons. When Hurricane Katrina hit, the levees failed at 53 separate points. Since the flooding, the federal government authorized more than $14 billion on new floodwalls.
With that money, the Army Corps of Engineers built the levees stronger and taller, to a standard they call “the best risk reduction system the Greater New Orleans area has ever had.”
They built new levees and also built in new safety features. In the Katrina flooding, water that washed over the levees also washed away the supporting soil on the inner side of the wall, causing the levees to collapse altogether. The engineers built in concrete splash pads over the vulnerable soil, meaning that it will stay and support the levee longer. They also built higher levees, where they could be built up, and deeper pilings to keep them upright.
Lake Borgne Surge Barrier is one of the crowning jewels of the system. At 26 feet tall and almost 2 miles long, it’s built to prevent storm surges from traveling up Lake Borgne onto land. The safety features protecting it are impressive: protective armor over the soil on both sides, support piles reaching more than 100 feet down into the ground and batter pilings to support the levee from behind.
The barrier is impressive, but it’s not perfect. It’s built for a 100-year storm, or a storm with a 1 percent chance of occurring in any given year. Katrina sent waves higher than the barrier. With global climate change driving stronger storms and higher sea levels, even higher waves are possible.
“Climate change is turning that 100-year flood, that 1 percent flood, into a 5 percent flood or a 20-year flood,” storm surge expert Rick Luettich told the New York Times.
This means that rarer storms, like 200 or even 500-year storms, could become more popular as well.
Like the surge barrier, most of the flood-protection system is built to a 100-year-storm standard. The reasons behind this are more political than engineering-based.
After Katrina’s flooding, a study by a team of Dutch engineers found that Central New Orleans should probably have protection against a 5,000- year storm. The federal government developed a three-stage funding measure for storm repairs. First, repair the broken walls and levees to pre-flood operations. Second, develop interim protection to a 100-year standard. Third, develop a plan for storm surges from a Category 5 Hurricane. As the Army Corps built up the interim protection, a congressional compromise meant that the city would be eligible for federal flood insurance when the 100-year protection was in place. It’s now locally known as the devil’s bargain because it meant that the 100-year standard became the norm.
Not everyone thinks it’s good enough.
“What we should have done was build to a 10,000-year flood standard, which is what the Netherlands built to, and we didn’t,” said Mitch Landrieu, former mayor of New Orleans. “That was for the country a monetary decision.”
Down the Drain
While the floodwalls get more attention, New Orleans’ drainage system is complex and fascinating. In addition to water washed over the city’s external defenses, the system has to contend with sudden heavy rains.
The drainage system starts when rain flows into catch basins. It is then fed through small pipes to larger pipes and canals, aboveground or underground. From there, the rainwater goes to pump stations. These stations still use the Wood Screw Pumps designed in 1913 by future water board superintendent A. Baldwin Wood. The pumps use a combination of a motor and vacuum pump to move water from a basin on one side of the station to a higher-elevation basin on the other side. In this case, through outfall canals to Lake Pontchartrain.
Because of their age, the pumps operate on 25-cycle power instead of the more typical 60-cycle electricity used in residences. This means that the city’s Sewerage and Water Board (S&WB) has its own generating stations.
According to city officials, the drainage system can handle an inch of rain during the first hour of a storm and a half inch every hour afterwards, which is approximately a 10-year storm. Last August, a 10-year storm left the city flooded.
Residents were furious. The S&WB hired independent consulting firm ABS Group to write a report on what exactly had gone wrong. The final report blamed clogged catch basins and too-small pipes due to delayed repairs and upgrades. It also placed a large share of the blame on the pumps. In the midst of the storm, multiple pumps weren’t operating at capacity because of power failures. The city’s independent generating stations went down, meaning that the S&WB only had about 10 percent of its power available. One of the city’s largest pumps stayed completely offline for six hours, leaving its station operating at less than two-thirds capacity.
Engineer Matt McBride also issued an independent report, focussing largely on the pump system. McBride’s report brought up the terrifying concept of reverse flow, where out-of-power drainage pumps start going backward, pumping water out onto the streets.
“The effect is frightening and disturbing, as swimming pools full of water are directed back into a neighborhood in an instant during a downpour,” McBride said in his report. “The force and speed of the flow can be so great that manhole covers are blown a dozen feet in the air blocks away from the reverse flowing pump.”
While McBride wasn’t able to conclusively prove that one of the stations experienced reverse flow, he pointed to station notes that might indicate reverse flow and that the power losses were a kind that could induce reverse flow.
Since the flood, S&WB’s leadership has largely retired. The agency has poured $82 million into system repairs and upgrades, including backup generators. The report also said that the city’s system wouldn’t be able to keep up with a 10-year storm even if it were operating at full capacity.
Part of the problem is that New Orleans is still relying almost totally on its “grey” water infrastructure, like pumps and pipes, and not new “green” water infrastructure. Green infrastructure focuses on redirecting the water through the environment and absorbing it into the soil. It includes things like rain gardens, porous pavement and bioswales, sloped drainage courses filled with vegetation to slow down water.
The federally funded Greater New Orleans Urban Water Plan urges a switchover to green water management. Municipal politicians are warming to the idea as well.
Why hasn’t the city made the switch? Politics and money.
In the wake of Hurricane Katrina, the Federal Emergency Management Agency (FEMA) gave a $2 billion grant to the city strictly for specific projects. Repairs and updates were delayed for years because of the political back-and-forth between FEMA and the city. Municipal politicians are worried about causing further delays by trying to get green projects approved and even more worried about the potential that FEMA could revoke funding. It’s a real risk, especially since FEMA is investigating the city to ensure it isn’t using any of the grant money on areas that were already in poor condition before the flooding.
“Can we [incorporate green infrastructure]? We’re looking,” Deputy Chief Administrative Officer Ramsey Green told The Lens. “We’re not going to jeopardize our funding. We have to be very cautious of slowing anything down.”
What Next?
Despite the recent repairs to the city’s water infrastructure, New Orleans’ future is still uncertain. Money, politics and the sheer difficulty of protecting a below-sea-level city in the age of global warming have meant that it’s difficult to build a system secure enough to handle the storms that might be coming.
Residents are fatalistic, and few trust the city after Katrina and the failures last August. Many believe that, in the next big storm, they’ll be out to sea.